1. Field of the Invention
This invention relates to a shaft bearing member having an oil groove formed in an inner circumferential face or sliding surface so as to circumferentially extend.
2. Description of the Related Art
Multiple cylinder engines for automobiles comprise a balance shaft provided in parallel with a crankshaft so as to be linked with the crankshaft in rotation so that vibration caused in the engine is reduced, for example. A plain bearing is usually used as a shaft bearing for bearing the balance shaft. Even if the balance shaft can reduce the vibration produced by the overall engine, the engine suffers a frictional loss due to the balance shaft with addition of a bearing for the balance shaft. Accordingly, provision of the bearing for the balance shaft becomes a disadvantageous condition. As a result, a reduction in the frictional loss in the bearing for the balance shaft has been desired.
Therefore, an object of the present invention is to provide a shaft bearing member which can reduce the frictional loss with rotation of the shaft.
The present invention provides a shaft bearing member for supporting a shaft so that the shaft is rotatable, the shaft bearing member having an inner circumferential face serving as a sliding surface. The shaft bearing member comprises an oil groove formed in the inner circumferential face so as to circumferentially extend, and a plurality of narrow grooves formed on the inner circumferential face so as to extend at a predetermined angle relative to a rotation direction of the shaft from at least one of both widthwise sides of the oil groove toward an axial end side of the inner circumferential face with respect to the shaft, the narrow grooves guiding a lubrication oil from the oil groove toward the axial end side with rotation of the shaft, the narrow grooves being shallower and narrower than the oil groove.
The lubrication oil supplied to the oil groove of the shaft bearing member flows through the oil groove onto the sliding surface with rotation of the shaft. An oil film pressure produced between the shaft and the sliding surface separates the shaft from the sliding surface. The inner circumferential face serving as the sliding surface has the plurality of narrow grooves formed thereon so as to extend at a predetermined angle relative to a rotation direction of the shaft from at least one of both widthwise sides of the oil groove toward an axial end side of the inner circumferential face with respect to the shaft. The narrow grooves guide a lubrication oil from the oil groove toward the axial end side with rotation of the shaft. The narrow grooves are shallower and narrower than the oil groove. Accordingly, the lubrication oil in the oil groove more easily tends to flow through the narrow grooves toward the axial end side of the sliding surface, thereby facilitating formation of oil film. Consequently, the frictional loss resulting from rotation of the shaft can be reduced since a direct contact between the shaft and the sliding surface is avoided.
To achieve the same object, the invention also provides a shaft bearing member for supporting a shaft so that the shaft is rotatable, the shaft bearing member having an inner circumferential face serving as a sliding surface. The shaft bearing member comprises an oil groove formed in the inner circumferential face so as to circumferentially extend, and a plurality of narrow grooves formed on the inner circumferential face so as to extend obliquely relative to a rotation direction of the shaft from both widthwise sides of the oil groove toward both axial ends of the inner circumferential face, the narrow grooves guiding a lubrication oil from the oil groove toward the axial end side with rotation of the shaft, the narrow grooves being shallower and narrower than the oil groove. In this construction, too, the inner circumferential face serving as the sliding surface has the plurality of narrow grooves formed thereon to extend from both widthwise sides of the oil groove toward both axial ends of the inner circumferential face obliquely relative to the direction of rotation of the shaft, the narrow grooves introducing the lubrication oil from the oil groove toward the axial end side with rotation of the shaft, the narrow grooves being shallower and narrower than the oil groove. Accordingly, the lubrication oil in the oil groove more easily tends to flow through the narrow grooves toward the axial end side of the sliding surface, thereby facilitating formation of oil film.
In a first preferred form, the shaft bearing member further includes a portion where no narrow groove is formed, said portion being located near the axial end of the inner circumferential face. Consequently, the shaft can be supported well since the oil film is desirably formed on the portion of the shaft bearing member where no narrow groove is formed.
In a second preferred form, the shaft bearing member further includes an escape portion formed near the axial end of the inner circumferential face so as to retreat radially outward. When the shaft swings with an axial inclination, there is a possibility that the shaft may locally contact both axial ends of the shaft bearing member. In view of this local contact, when the escape portion is formed near the axially outer end of the inner circumferential face, an occurrence of the local contact between the shaft and sliding surface can be prevented.
In a third preferred form, the shaft bearing member is formed into a generally semicylindrical shape and has the plurality of narrow grooves in a circumferentially central portion of the inner circumferential face thereof and portions where no narrow groove is formed, said portions being located near both circumferential ends of the inner circumferential face thereof respectively. When two semicylindrical shaft bearing members are combined together into a cylindrical bearing shaft member, the lubrication oil disadvantageously tends to flow out of the circumferential ends. However, since no narrow grooves are formed in the portions located near both circumferential ends, the lubrication oil can be prevented from flowing out of the circumferential ends.